The subject of the present invention is an autonomous electrically powered vehicle that, to power it, requires a significant mass and/or volume of batteries, for example a utility vehicle or a public transport vehicle.
In spite of the availability of high-performance batteries (NiMH, lithium-ion, etc.), it is practically impossible to design autonomous vehicles with a large payload capability and which are “all electric”, because of the problems of storing the electricity and of the autonomy or range of the vehicle.
Furthermore, one serious obstacle to the introduction into service of electrically powered autonomous vehicles stems from the fact that the technological variation, in terms of batteries, is great, complex, expensive, rapidly surpassed and that the batteries usually require special equipment in servicing and repair shops. These constraints are incompatible with the need of the operators concerned with the transport of individuals and/or goods who need to amortize their investments in rolling stock over a period of between 10 and 20 years.
In order to alleviate the problems of storing electricity and of the autonomy or range of the vehicle, it is necessary at the present time for vehicles equipped with such batteries to be equipped with rapid recharging devices and/or with electric generator sets stored on board the vehicle and able to provide top-up power.
Electrically powered vehicles in which the batteries are installed on a trailer have also been conceived of, for example, in U.S. Pat. No. 3,690,397, DE-A-42 05 327, DE-A-41 05 246 or FR-A-2 482 528.
In the case of an electrically powered utility vehicle, it is necessary to be able to have a significant available energy capacity and therefore a sufficient volume of batteries (ranging between 1.5 and 3 m3). Technical progress means that the trend is for batteries to supply more power for, sometimes, less weight, but their volume remains more or less unchanged. With lead-acid batteries, a volume of about 2 m3 corresponds to a mass of about 3 metric tons.
The prior art recalled above discloses small trailers equipped with a single wheel (the aforementioned U.S. Pat. No. 3,690,397, DE-A-42 05 327 or DE-A-41 05 246), which solution cannot be read across to the trailer-mounting of a significant mass of batteries as mentioned hereinabove, because that would require the use of a wide (of the order of 400 mm wide) wheel of large (of the order of 1200 mm) diameter, the travel of which, if the wheel were to be a pivoting wheel as in U.S. Pat. No. 3,690,397, would considerably reduce the volume available for the batteries. Furthermore, even if the wheel were not a pivoting wheel, as in DE-A-42 05 327, the fact that there was only one wheel would present only disadvantages when applied to a connectable/disconnectable trailer:                lack of stability when handling,        the need to provide complicated, bulky and expensive guidance and suspension means,        the difficulty of maintenance, and        the difficulty of repairing it should it experience a flat.        
The aforementioned DE-A-41 05 246 discloses a trailer in which the, non-steered, wheel or wheels is or are situated between the, also non-steered, wheels of the vehicle and on the same transverse axis. The trailer is guided transversely but can move up and down vertically, an elastic device being positioned between the vehicle chassis and the trailer and acting as suspension.
However, this design operates correctly only under ideal conditions because:                when the trailer goes over a speed hump, it may be crushed by the chassis of the vehicle; and        when starting a bend with a cross-fall, the chassis of the vehicle will become inclined transversely with respect to the trailer and considerable loadings will be applied to the trailer transverse guidance device.        
In consequence, the operation of the device that forms the subject of DE-A-41 05 246 cannot be considered to be reliable.
The prior art (the aforementioned FR-A-2 482 528) also discloses the addition of a trailer, equipped with a two-wheeled axle, to a utility vehicle, but the size of this trailer is added to that of the vehicle, the result of this being a considerable loss of space when running around and at the depot.
Installing the batteries on an independent chassis makes it possible to conceive of forming, at the vehicle depot, a fleet of charged battery chassis for the purposes of exchanging charged battery chassis for battery chassis that are running out of power, but no document in the prior art either describes or suggests means for making the connecting and disconnecting of the trailer in order to perform such an exchange rapid, particularly when said trailer is situated under the chassis of the vehicle.